Circumferential Meniscal Extrusion Mapping Using Radial Multiplanar Reconstructions

Meniscal extrusion is a marker of meniscal dysfunction and has been associated with osteoarthritis progression. Assessment is typically performed on a single coronal magnetic resonance imaging (MRI) slice, but this method may miss the location of maximal circumferential displacement. We developed an extrusion mapping technique using radially oriented multiplanar reconstruction (rMPR) images from high-resolution 3D MRI to enable circumferential meniscal position measurements perpendicular to the tibial margin. Extrusion was measured by three independent readers on rMPR images generated from non-fat-saturated 3D fast spin-echo MRI in 20 patients stratified by meniscal tear and extrusion status. Intrareader and interreader measurement variabilities were assessed using intraclass correlation coefficient (ICC), 95% repeatability coefficient (RC; intrareader), and 95% reproducibility coefficient (RDC; interreader). Corresponding rMPR and standard 2D coronal midbody extrusion measurements were compared. Intrareader variability was low, with a mean within-meniscus within-angle standard deviation (SD) of 0.2 mm and mean RC of 0.6 mm. Interreader variability was also low, with a mean within-meniscus within-angle SD of 0.5 mm and mean RDC of 1.4 mm. At the midbody, there was 98% concordance for extrusion classification between rMPR and 2D coronal measurements within the interreader RDC (1.4 mm). Exploratory regional analysis suggested different extrusion patterns between medial and lateral menisci and between torn and intact menisci. These findings suggest that circumferential meniscal extrusion mapping using rMPR images from 3D knee MRI is feasible, with low intrareader and interreader measurement variabilities. This framework enables regional characterization of meniscal displacement and should support future investigations of meniscus-osteoarthritis relationships. STATEMENT OF CLINICAL SIGNIFICANCE: Meniscus extrusion circumferential mapping using radially oriented multiplanar reconstruction images is feasible and consistent across readers and allows a more complete assessment of meniscal position, which may be valuable for further investigation of meniscal injury and osteoarthritis.